1. Field of the Invention
The present invention relates to a running stability control of a vehicle, and more particularly, to a running stability control for a vehicle according to a control of the steering angle of the steered vehicle wheels and a control of the driving/braking force applied to the vehicle wheels.
2. Description of the Prior Art
For automatically controlling a running stability of a vehicle such as an automobile, it has been proposed, as described in Japanese Patent Laid-open Publication 2003-175749 of a patent application filed by the same applicant as the present application, to construct a running stability control device of a vehicle so as to modify the steering angle of the steered vehicle wheels independently of the steering operation by a driver, and control the driving/braking force applied to the vehicle wheels, by computing a target turn running control quantity such as a target yaw moment of the vehicle, sharing the target turn running control quantity into a first target turn running control quantity by a steering angle control of the steered vehicle wheels and a second target turn running control quantity by a control of the driving/braking force applied to the vehicle wheels according to a predetermined sharing ratio therebetween, and controlling the steering angle of the steered vehicle wheels based upon the first target turn running control quantity by the steering angle control of the steered vehicle wheels and the second target turn running control quantity by the control of the driving/braking forces applied to the vehicle wheels.
When the turn running stability of the vehicle is controlled by the control of the steering angle of the steered vehicle wheels, the turn running performance of the vehicle can be controlled not to affect the driving/braking forces applied to the vehicle wheels. However, the control of the steering angle of the steered vehicle wheels is slower in its response than the control of the running stability by the driving/braking forces applied to the vehicle wheels, and is not effective to overcome an understeered condition of the vehicle. In contrast, the running stability control by the control of the driving/braking forces applied to the vehicle wheels is high in its response as compared with the running stability control by the steering control of the steered vehicle wheels, but unavoidably affects a smooth running of the vehicle by an acceleration or a deceleration being induced in the vehicle.
According to the running stability control by the above-mentioned former proposal, the target turn running control quantity is shared into the first turn running control quantity for the steering angle control of the steered vehicle wheels and the second target turn running control quantity for the driving/braking forces applied to the vehicle wheels according to a ratio predetermined based upon the responsiveness and other features of the steering device and the driving/braking force control device, so that thereby the running stability of the vehicle can be more desirably and effectively controlled as compared with the control only by the steering angle control of the steered vehicle wheels or the control only by the driving/braking force control applied to the vehicle wheels.